Saturday, March 27, 2010

After a young, middle class couple moves into what seems like a typical suburban “starter” tract house, they become increasingly disturbed by a presence that may or may not be demonic but is certainly most active in the middle of the night.

Especially when they sleep. Or try to.

A new case study in Cortex by neurologist Dr. Fabienne Picard (2010) reports on a patient who experienced unusual phenomena during epileptic seizures. She had the convincing sense that several familiar people (family members) were standing before her. This experience of a "sensed presence" is a classic trope in movies with supernatural themes (e.g., Carnival of Souls[available at Internet Archive], The Haunting[trailer for the 1963 version], Poltergeist, Dark Water), but it's generally attributed to ghosts and not to seizure activity.

Here's the case report:

A 62-year-old right-handed woman of normal psychiatric history presented a simple focal epileptic seizure including a complex sensation characterized by feeling the presence of several members of her family in the immediate environment, associated with paresthesia of the right hemibody (excluding the face). The feeling of presences and the paresthesia (numbness) appeared concomitantly and lasted in total several minutes. The episode occurred while she was sitting alone on the sofa of her living room and immediately felt the presence of four persons in her frontal space. She did not see or hear these persons (no visual or auditory hallucinations), but felt vividly their presence in her peripersonal[within reach] and near extrapersonal space [just outside of reach]. She “recognized” them as close family members. Closest was her grand-daughter who was sitting on the floor immediately in front of her, without any left or right lateralization in relation to her body, whereas the three other persons, her daughter and two other grand-children, were experienced to be localized at a distance of several meters. ... This highly vivid and convincing feeling of presences was described by the patient as deeply pleasant, although she guessed that it was not possible that they were really there, as she was alone just before. ... She was treated with pregabalin (300 mg/day) and there was no recurrence of simple or complex partial seizures and no further feeling of presences.

MRIs revealed abnormal findings due to a right hemisphere subcortical stroke 10 months before the episode (Fig. 1A). The patient's stroke affected a portion of the basal ganglia (the putamen and the globus pallidus) and a large white matter tract within (the internal capsule). Left hemisphere findings in the insular cortex were also apparent, and this was the likely seizure focus. Strokes are known to increase the incidence of seizures: in one study 8.6% of those with ischemic stroke[occlusion of blood supply] and 10.6% of those with hemorrhagic stroke[bleed] had one or more seizures within a year (Bladin et al., 2000).

Fig. 1 (adapted from Picard, 2010).FLAIR coronal MR images of the patient. (A)two days after a right capsulo-lenticular haemorragic stroke. (B)ten months later, at the time of the episode of feeling of presence. In addition to the right capsulo-lenticular sequela extending to the insula, a hypersignal is visible in the white matter/grey matter border of the left insular region [already visible in (A)], as well as a diffuse corticosubcortical atrophy, predominating in the right hemisphere, and a leukoencephalopathy[white matter disease].Picard (2010) thinks this particular case is unique and not a more typical disorder of body perception:

Most authors consider the feeling of a presence (FP) as a disorder of own body perception, an illusory reduplicative phenomena involving the self. Thus FP would be akin to the three main forms of autoscopic phenomena (seeing a double of oneself) which include a) out-of-body experience. The subjects appear to see themselves and the world from a location above their physical body. The self is localized outside one's physical body (disembodiment); b) autoscopic hallucination, which consists of seeing one's body in extracorporeal space (as a double) without disembodiment; and c) heautoscopy, an intermediate form between out-of-body experience and autoscopic hallucination.

Instead, the felt presence was more akin to a "hallucination" for known people going about normal daily activities. Nonetheless, involvement of the insula, important for interoceptive awareness of bodily states (Craig, 2009), is still suggestive of a disruption in the sense of self and its interaction with the external world.

To end our story, the patient's experience of a sensed presence did not recur once her seizures were controlled with medication. A short neurological horror film resolved by prescription of an anticonvulsant drug might not be a strong sell in Hollywood.

Wednesday, March 24, 2010

"Voodoo correlations in social neuroscience" was the original title of a paper that first caused a stir in late December 2008, when a manuscript accepted by Perspectives on Psychological Science was made available on the authors' websites. Vul, Harris, Winkielman, and Pashler produced a "bombshell of a paper" that questioned the implausibly high correlations observed in some fMRI studies in the field of Social Neuroscience. Ed Vul et al. surveyed the authors of 54 papers to determine the analytic methods used. All but three of the authors responded to the survey, and 54% admitted to using faulty methods to obtain their results:

More than half acknowledged using a strategy that computes separate correlations for individual voxels, and reports means of just the subset of voxels exceeding chosen thresholds. We show how this non-independent analysis grossly inflates correlations, while yielding reassuring-looking scattergrams. This analysis technique was used to obtain the vast majority of the implausibly high correlations in our survey sample. In addition, we argue that other analysis problems likely created entirely spurious correlations in some cases.

Here we have a public debate between Dr. Piotr Winkielman, one of the authors of the Voodoo paper (Vul et al. 2009, PDF), and Dr. Matthew Lieberman, one of the accused (rebuttal: Lieberman et al. 2009, PDF) at the 2009 meeting of the Society of Experimental Social Psychologists. Dr. Lieberman has made these videos and papers available on his website, and I thank him for drawing my attention to them.The Voodoo Debate Continues...

Lieberman did strike back (Lieberman et al., 2009), and attacked Vul et al. for cherry picking their data and for inappropriate use of statistics:

However, they imply that post hoc reporting of correlations constitutes an invalid inferential procedure, when in fact it is a descriptive procedure that is entirely valid. In addition, the quantitative claims that give their arguments the appearance of statistical rigor are based on problematic assumptions. Thus, it is ironic that Vul et al.’s article—which critiques social neuroscience as having achieved popularity in prominent journals and the press due to shaky statistical reasoning—itself achieved popularity based on problematic claims about the process ofstatistical inference.

Our previous post (Friston is Freudian) presented an overview of the new megawork [metawork?] of Carthart-Harris & Friston (2010), an ambitious project to map selected Freudian ideas (id and ego but not super-ego)1 onto the brain's large-scale intrinsic networks as revealed by modern neuroscientific methods (fMRI, resting state functional connectivity, intracranial EEG recordings, and computational models). As mentioned before, they marshalled the neuroscientific concepts of Bayesian Brain, Default Mode Network, Free Energy, Gamma Oscillations, Prediction, Prediction Error, Theta Oscillations, and Top-Down Control in support of their neuropsychoanalytic scheme. After reading the article, I was amazed at the boldness and creativity it took to develop this framework. The 70 pages of Supplementary Data included 493 quotes from Freud.

Freud's Model of the Mind: "The ego is not sharply separated from the id; its lower portion merges into it.... But the repressed merges into the id as well, and is merely a part of it. The repressed is only cut off sharply from the ego by the resistances of repression; it can communicate with the ego through the id." (From Freud's 1923 paper "The Ego and the Id")

However, not all 493 quotes were used in support of selected characteristics of the ego (Secondary Process - ‘normal waking consciousness of adult humans’) and the id (Primary Process - ‘altered’ or ‘non-ordinary’ states of consciousness). For instance, I don't see Q439 (on early childhood sexuality) anywhere in Table 1 or the text:

The sexual life of human beings exhibits an efflorescence which comes to an end at about the fifth year and it followed by what is known as the period of latency (till puberty)… [Q439, Freud, 1939, p. 75]

Likewise, the super-ego is neglected (see also Footnote 1):

If we consider once more the origin of the super-ego as we have described it, we shall recognise that it is the outcome of two highly important factors, once biological and the other of a historical nature: namely, the lengthy duration in man of his childhood helplessness and dependence, and the fact of his Oedipus complex, the repression of which we have shown to be connected with the interruption of libidinal development by the latency period and so with the diphasic onset of man’s sexual life... [Q344, Freud, 1923, p. 35]

But let's return to what they did include in their synthesis. C-H and F want to establish the construct validity of Freudian concepts (id and ego) to operationalize them and subject them to empirical scrutiny. In brief, the ego (normal adult human consciousness) is more or less equated with activity in the brain's "default mode" network (Raichle et al., 2001), measured as spontaneous fluctuations in the BOLD signal during unconstrained cognition. Activity in the default mode network (DMN)2 is anti-correlated with activity in "active task" networks, which are engaged by typical neuroimaging experiments. In contrast to the ego, the limbic id is equated with unusual and altered states of consciousness, as seen in psychosis, the aura of temporal lobe epilepsy, hallucinogenic states, and REM sleep.3

Added to this is a key concept in recent Fristonian thought. The "free-energy principle" is the idea that the brain is an inference engine (Helmhotz, 1860) that makes probabilistic predictions about the world (i.e., its external and internal input) based on past experience, then updates these predictions based on current events (Friston, 2010). The goal is to minimize "free-energy"4 or prediction error.

The emerging picture is that the brain makes its inferences by minimizing the free-energy of messages passing between hierarchical brain regions. ... Information from these exchanges passes on to “higher” levels (those responsible for cognitive functions) through “bottom up” connections. The higher levels respond with “top down” messages to the lower levels. This reciprocal exchange repeats itself hierarchically, back and forth, layer by layer, until the highest level ... becomes engaged. Only then will you consciously register a perception. In this scheme, the free-energy is essentially the collective prediction error over all levels of the hierarchy: Top-down cognitive messages provide predictions based on representations from above, and lower sensory levels reciprocate with bottom-up prediction errors. These “error messages” drive encoded representations (such as neuronal activity) to improve the predictions for lower levels (that is, to reduce free-energy).

Friston’s ideas build on an existing theory known as the “Bayesian brain”, which conceptualises the brain as a probability machine that constantly makes predictions about the world and then updates them based on what it senses.

The idea was born in 1983, when Geoffrey Hinton ... and Terry Sejnowski ... suggested that the brain could be seen as a machine that makes decisions based on the uncertainties of the outside world. In the 1990s, other researchers proposed that the brain represents knowledge of the world in terms of probabilities. Instead of estimating the distance to an object as a number, for instance, the brain would treat it as a range of possible values, some more likely than others.

A crucial element of the approach is that the probabilities are based on experience, but they change when relevant new information, such as visual information about the object’s location, becomes available. “The brain is an inferential agent, optimising its models of what’s going on at this moment and in the future,” says Friston. In other words, the brain runs on Bayesian probability. Named after the 18th-century mathematician Thomas Bayes, this is a systematic way of calculating how the likelihood of an event changes as new information comes to light.

How are all of these biological and mathematical observations related to Freudian psychology? The helpful table below gives a summary.

The overlapping phenomenology of REM sleep, early and acute psychosis, the temporal lobe aura and the hallucinogenic drug state.

All these states have been independently compared with each other previously and described independently as conducive to primary process thinking.

The neurophysiology of these non-ordinary states is remarkably consistent both empirically and with Freud’s descriptions of the ‘free-flowing’ energy of the primary process.

LSD given immediately prior to or during sleep promotes REM sleep.

The overlap between Freud’s descriptions of the give-and-take relationship between ego–libido and object–libido and the give-and-take relationship between the DMN and its anti-correlated networks.

The concordance between Freud’s descriptions of the secondary process working to minimize free-energy and the free-energy account of the hierarchical organization of intrinsic networks working to minimize prediction errors.

The integrated, compound nature of the DMN and Freud’s descriptions of the integrated, compound nature of the ego.

The development of functional connectivity between the nodes of the DMN during ontogeny, a process that parallels the emergence of ego-functions.

Freud’s account of the ego as a recipient and product of regular endogenous activity concerned with drive, memory and affect and the functional and structural connectivity of the DMN’s cortical nodes with limbic structures concerned with drive, memory and affect.

Freud’s description of the ego as a tonic reservoir of activity and the high resting-state metabolism of the DMN.

Freud’s account of the ego as the seat of the sense-of-self and studies showing increased activity in the DMN during self-referential processing and a failure to deactivate the DMN in pathology characterized by withdrawal.

After reading the 10 page presentation of this formidable new framework for the mind we come to the Discussion, where Carthart-Harris and Friston make some concessions:

"For those opposed to Freud, who would rather see his constructs dissolved into pure phenomenology and neurobiology, we put up little resistance (e.g. Q176). Phenomenology and neurobiology can stand alone."

In essence what we've seen here is a surprising form of Reverse Reductionism, or Expansionism: a mapping of brain states onto the concepts of id and ego. Am I the only one who is unaware of this new trend in neurosciences/cognitive sciences? Although it is an impressive and scholarly treatment of Freud in light of the latest neurophysiological and computational principles, one can view the entire synthesis as a series of metaphors. The authors concede as much:

"If [Freud’s theories] were built on false inference and loose philosophy, it is unlikely they would have endured in the way that they have."

Just because the Freudian view has persisted doesn’t mean it’s correct. What about creationism? Or intelligent design? While we're on the topic of pseudoscience, are some of the less "scientific" interests of Freud (e.g., telepathy) irrelevant here? It seems to me that picking and choosing which Freudian ideas you want to implement in the brain and which you want to discard is akin to picking and choosing which biblical laws in Leviticus you do (or do not) want to follow.

Freud's theory implies that the super-ego is a symbolic internalization of the father figure and cultural regulations. ... The super-ego acts as the conscience, maintaining our sense of morality and proscription from taboos. Its formation takes place during the dissolution of the Oedipus complex and is formed by an identification with and internalization of the father figure after the little boy cannot successfully hold the mother as a love-object out of fear of castration.

...The concept of super-ego and the Oedipus complex is subject to criticism for its sexism. Women, who are considered to be already castrated, do not identify with the father, and therefore form a weak super-ego, leaving them susceptible to immorality and sexual identity complications.

3 These altered states of consciousness were viewed in an interchangeable fashion and related to hippocampal theta activity. Does this mean that spatial navigation, learning, and memory are considered primary process modes of thought?

4 "An information theory measure that bounds or limits (by being greater than) the surprise on sampling some data, given a generative model" (Friston, 2010).

Friday, March 12, 2010

Professor Karl Friston is one of the most prominent (and prolific) researchers in the field of neuroimaging. His contributions to methodological development in functional magnetic resonance imaging (fMRI) are immense:

He invented statistical parametric mapping; SPM is an international standard for analysing imaging data and rests on the general linear model and random field theory (developed with Keith Worsley). In 1994, his group developed voxel-based morphometry. VBM detects differences in neuroanatomy and is used clinically and as a surrogate in genetic studies... In 2003, he invented dynamic causal modelling (DCM), which is used to infer the architecture of distributed systems like the brain. Mathematical contributions include variational filtering and dynamic expectation maximization (DEM) for Bayesian model inversion and time-series analysis.

Psychoanalysis has had a turbulent and complex relationship with neuropsychology for the century in which the two fields have existed – largely side by side. Some within the neuroscientific community have found much of value in Freudian ideas – Paul Schilder springs to mind as an early example, with Eric Kandel as the most prominent recent advocate (Kandel, 1999). However, for most neuropsychologists, indeed for most scientists, the obvious response to the mention of psychoanalysis has been one of blanket rejection.

With respect to dreams, Sigmund Freud was not only not right. He was dead wrong. And so are Turnbull and Solms (2007) in their desperate effort to save Freudian psychoanalysis from the junk heap of speculative philosophy. Neuroscientists, psychologists, and psychiatrists beware: you are being led down the garden path by this pair of misguided neo-Freudians.

It is with this stormy background in mind that one should embark on reading the Brain paper. Mercifully, for those lacking the mathematical background to understand even the most rudimentary quantitative formulation of Friston's free-energy principle (2009, 2006), the paper is free of equations. No matter what you think of the final result, it's an intellectual tour de force with 493 quotes from Freud in 70 pages of Supplementary Data. Essentially, the approach is to take a collection of cutting-edge and trendy ideas in neuroscience and map them onto Freud's id and ego. For your convenience, here is a list of the main neuroscientific concepts:

Bayesian Brain

Default Mode Network

Free Energy

Gamma Oscillations

Prediction

Prediction Error

Theta Oscillations

Top-Down Control

You might be saddened by the lack of mirror neurons, social cognition, and empathy in the current conceptualization. But it should be all about sex, right? Well, actually, Carhart-Harris and Friston are much more chaste in their mapping of Freudian ideas onto neurobiology and default mode function. The words sex, sexual, sexuality (and any variants) appear zero times in the Brain article, but 18 times in the collection of Freud quotes. The word libido was mentioned 112 times in the Freud quotes but only 4 times by the present authors [excluding reproduction of Freud quotes in the main text].

For "accessibility" cathexis was interpreted in a generic (not specifically sexual) sense to mean activation or energy. But according to Freud, mental energy is the id, the psychic energy that powers the mind:

Freud defined Libido as the instinct energy or force. Freud later added the Death drive (also contained in the id) as a second source of mental energy.

Next time we'll take a closer look at this ambitious synthesis of psychoanalysis and neuroimaging.

Friday, March 05, 2010

Author and blogger Jonah Lehrer has a lengthy (and controversial) essay in the Feb. 28 New York Times Magazine on Depression's Upside. The main idea, that depression has cognitive and evolutionary advantages, was largely based on a review paper by Andrews and Thomson (2009). In it, they put forth the analytical rumination hypothesis: depression is an evolved response to complex problems, and focusing on them to the exclusion of everything else is beneficial. Lehrer's piece generated an outpouring of comments (both pro and con), questions, and critiques. One notably critical rejoinder (The Myth of Depression’s Upside) was written by Dr. Ronald Pies, the Editor in Chief of Psychiatric Times:

Now, with all due respect to Dr. Thomson, I am inclined to ask, “[Insights gained during depression are] worth it to whom?” Perhaps the patients Dr. Thomson has treated emerge from their three-month bouts of depression saying, “Ya know what, Doc? It’s been a bad three months—lost my job, almost killed myself, and couldn’t get a damn thing done—but overall, it was worth it!” The depressed patients I evaluated over the past nearly 30 years almost never reported that their major depressive episodes had a “net mental benefit,” to quote Lehrer’s article. Most felt that their lives and souls had been stolen from them for the duration of their depressive episode.

In other words, Dr. Pies's patients don't feel like they've solved all their problems. Most of the studies cited in favor of improved problem-solving abilities involved a sad "mood induction" procedure such as watching a 10 min film showing a death from cancer or being given false negative feedback on cognitive test performance (Forgas, 2007). It should be obvious that a transient, slightly sad state is drastically different from a prolonged major depressive episode. Jonah does acknowledge this in his article, but the distinction appears to undermine Andrews and Thomson's entire basis for asserting analytical advantages for the depressed ruminator. It's another in a long line of evo psych just-so stories.

The end result is poor performance on tests for memory and executive function, especially when the task involves lots of information. (These deficits disappear when test subjects are first distracted from their depression and thus better able to focus on the exercise.)

On the contrary, numerous papers have shown that impairments in cognitive processes such as executive control, attention, and memory persist after a depressed person has recovered (Andersson et al., 2010; Baune et al., 2010; Hammar et al., 2009). In actively depressed patients, Baune and colleagues (2010) found impairments in all domains tested: immediate memory, visuospatial construction, language, attention, and delayed memory. These deficits can contribute to lower social and occupational functioning and a diminished quality of life. In addition, depression can be associated with declines in problem solving abilities on neuropsychological tests such as the Wisconsin Card Sorting Test and the Tower of London test.

A recent review of the literature provided additional support for the existence of pervasive cognitive deficits (Hammar et al., 2009):

Research during the past decade has mainly focused on cognitive functioning in the severe phase of depression, and today it is widely accepted that the disease is characterized by cognitive impairment in the acute state. There are reports of findings in different cognitive domains, such as executive functions, attention, memory and psychomotor speed.

Well (you say), what about Social Dilemmas? Aren't these different from the Stroop task? The Psych Review manifesto on the Bright Side of Being Blue states that "Complex social problems may be the primary evolutionarily relevant trigger of depression in human beings." But support for the view that depression improves the ability to solve such problems is meager, apparently consisting of two old papers (Hokanson et al., 1980; Pietromonaco & Rook, 1987). The Hokanson paper turns out to be not-so-great for the analytical rumination hypothesis: (1) The "depressed" group had scores on the Beck Depression Inventory of 10 or greater, which includes those with only very mild depression. (2) Ironically, Hokanson et al. view their own results as evidence of social skills deficits, not enhanced social problem solving:

If, indeed, depressed individuals display different social responses, depending on situational or social role variables, one might expect that real-world relations are characterized by contradictory behaviors, mixed messages, emotional ambivalence, and so forth. Such stimulus arrays may indeed evoke several competing response tendencies in others, a situation that a simple reinforcement-punishment view would be hard pressed to handle.

This work suggests that depressives' cognitive analysis of common life situations leads them to make decisions that promote their social isolation and, thereby, perpetuate their depression.

The analytical rumination hypothesis even has the potential to be harmful. Belief in the glorious "upside" of their ailment could prevent some severely depressed individuals from getting proper treatment, placing them at greater risk of suicide and other adverse events. Needless to say, such an outcome would be of no evolutionary advantage.

Below is a box/blob and arrow diagram of the analytic rumination model (click on image for a larger view). A critique of its ludicrous biological underpinnings is beyond the scope of this post.

Figure 1 (Andrews & Thomson, 2009). A diagram of the proposed causal relationships between the variables and the constructs that are prominent in the analytical rumination hypothesis. The diagram uses the terminology of structural equation modeling [NOTE: but none of its quantitative rigor], with the circles representing latent constructs, the rectangles representing manifest variables, and the arrows denoting the hypothesized direction of causation. The plus (+) sign denotes a positive or facilitative causal relationship between variables, and the minus (-) sign denotes a negative or inhibitory causal relationship. 5-HT = 5-hydroxytryptamine or serotonin; L-VLPFC = left ventrolateral prefrontal cortex; R-VLPFC = right ventrolateral prefrontal cortex; WM = working memory.

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Tuesday, March 02, 2010

In the last post we learned about Alice in Wonderland syndrome, a rare phenomenon involving distortions of visual perception and body image, most often caused by migraines. Although a specialty practice in headache might seem dull [so to speak] at first glance to those interested in behavioral neurology, unusual and colorfully-named types of headaches can make things more interesting. In Case Studies of Uncommon Headaches (2006), Dr. Randolph Evans reviews a number of these unfortunate ailments, which include exploding head syndrome, neck-tongue syndrome, red ear syndrome, and burning mouth syndrome. So let's begin with a hot ear.

Case 6. My ear is red, hot, and burning

A 54-year-old white woman was seen who had a 10-year history of episodes of a burning sensation of the left ear. The episodes are preceded by nausea and a hot feeling for approximately 15 seconds and then the left ear becomes visibly red for an average of approximately 1 hour, with a range of approximately 30 minutes to 2 hours. Approximately once every 2 years, she had a flurry of episodes occurring over approximately a 1-month period during which she averaged approximately five episodes, with a range of 1 to 6.

There also was an 18-year history of migraine without aura occurring approximately once a year. ... A cerebral arteriogram revealed a proximal left internal carotid artery occlusion of uncertain cause after extensive testing. MRI scan at age 45 was normal. Neurologic examination was normal. A carotid ultrasound study demonstrated complete occlusion of the left internal carotid artery and a normal right.

It can also occur in association with migraines, glossopharyngeal and trigeminal neuralgia, upper cervical spine pathology, and herpes zoster[shingles]. The GABA analogue and anti-seizure medication gabapentin can be helpful in preventing RES.

By the way, the girl in the picture above[who is not Case 6] says her red ear doesn't hurt, and that she doesn't get headaches.

Case 7. My mouth is burning

A 49-year-old woman was referred by her primary care physician with a 1.5-year history of daily constant burning or numbness of the entirety of her tongue and the back of her throat. She also complains that the inside of her mouth is sensitive. She has had a dry mouth for the past year. ... Artificial saliva has not been helpful. She has tried a variety of pain pills without any help....

Burning Mouth Syndrome1 most often afflicts middle-aged and older women. Causes include dry mouth (e.g., from medications or diabetes), nutritional deficiency, food allergies, fungal infection (candidiasis aka thrush), trigeminal small fiber neuropathy (nerve damage), and hormonal changes. Treatments range from estrogen-progesterone replacement therapy to nutritional supplements to switching prescription medications to addressing an underlying medical condition. I don't know if this syndrome can be considered a "headache" in the standard usage of the word, but then again I'm not a neurologist.

Case 1. Noises in the night

A 43-year-old woman was seen with a 5-month history of a noise in her head. On an almost nightly basis, as she was falling asleep, she would hear a loud noise like "electrical current running" lasting a second. Sometimes her whole body would shake for a second afterwards. Very occasionally, she would have an associated flash of light. Frequently, a second episode of the loud noise occurred shortly after the first. She then could fall asleep without any problem.

Exploding Head Syndrome (Pearce, 1988) is a bang-up way to be aroused from your nightly slumber. A small percentage (~10%) of sufferers see a flash of light, even fewer feel as if they've stopped breathing for a short time. It's more frightening than it is painful. Interestingly, Evans (2006) suggests that EHS might be caused by delay in the reduction of activity in the brainstem reticular formation as the patient transitions from wakefulness to sleep. In 1949, Moruzzi and Magoun were the first to recognize that stimulation of the brainstem reticular formation produces low-voltage fast activity in the EEG, characteristic of an alert and attentive behavioral state. So something might be neurologically amiss with the EHS patient's sleep-wake cycle, although Evans gave no direct evidence of this. And the explosion phenomenology is largely unexplained, as noted by Pearce (1988):

The cause of the bomb-like noise remains a mystery: no known vascular or hydrodynamic changes in the brain, labyrinths, or cerebrospinal fluid would cause such a symptom, although a momentary (almost ictal) disinhibition of the cochlea or its central connections in the temporal lobes, or a sudden involuntary movement of the tympanum or tensor tympani, might be the explanation...

About Me

Born in West Virginia in 1980, The Neurocritic embarked upon a roadtrip across America at the age of thirteen with his mother. She abandoned him when they reached San Francisco and The Neurocritic descended into a spiral of drug abuse and prostitution. At fifteen, The Neurocritic's psychiatrist encouraged him to start writing as a form of therapy.